This research involves: (1) studies on human and mouse cells bio-chemically transformed to the thymidine kinase (TK)-positive phenotype by herpesvirus TK genes; and (2) studies on the significance of the "early region" of the SV40 genome for the maintenance of the transformed phenotype. A clone-purified Pvu II fragment of HSV-1 DNA, which codes for TK, is being used to analyze the interaction of the TK gene with RNA polymerase and the regulatory alpha protein, VP175, which is coded by HSV-1 (KOS) gene B. Since the PRV II fragment also codes for a herpesvirus-associated nuclear antigen (HANA), experiments are being carried out to learn whether HANA maps to the right of TK, is on the same DNA sequence as TK but is translated from a different mRNA from the mRNA that codes for TK, or whether HANA and TK are one and the same. The marmoset herpesvirus restriction nuclease fragment that codes for TK has been identified. It will be cloned in an E. coli plasmid and its position on the physical map of marmoset herpesvirus DNA will be ascertained. Recombinants containing herpesvirus TK and SV40 DNA sequences will be used to biochemically transform human cells. Conditions will be sought which would permit the recombinant DNA to replicate extrachromosomally. The possible methylation of SV40 and herpesvirus TK DNA sequences in biochemically transformed cells will be studied.